A radio-frequency signal to be transmitted is normally amplified in the front end of a mobile radio before it is emitted via an antenna. The transmission is normally at a variable radio-frequency output power. This is matched, inter alia, to external characteristics such as the distance to a base station at that time.
In modern third-generation mobile radios which operate on the basis of the UMTS (Universal Mobile Telecommunications Standard) mobile radio standard, the radio-frequency output power has to be variable over a very wide range. For example, a specification might require a “worst case” gain range of 83 dB. To achieve such rates so-called VGA, Variable Gain Amplifier, are typically provided in the transmission path of a corresponding communication appliance. An external control voltage is normally used to control the gain of this amplifier, with a signal to be transmitted being amplified as a function of this control voltage. Curve 1 in FIG. 3 shows a typical probability distribution of different output power requirements.
Furthermore, whenever the gain of the amplifier is changed, there is a need for maintaining carrier signal suppression. Also, the mean power consumption over a predefined statistical output power probability should be minimal. Thus, a maximum standby and usage time for mobile phones can be obtained.